Electric guitar piezoelectric transducer bridge with replaceable string height adjustors



Sept. 22, 1970 R, c. sc 3,530,228

ELECTRIC GUITAR PIEZOELECTRIC TRANSDUCER BRIDGE WITH REPLACEABLE STRINGHEIGHT ADJUSTORS Filed April 23, 1968 INVENTOR 16 ROBERT C. SCHERER 1 2I BYM/ ATTORNEYS United States Patent O 3,530,228 ELECTRIC GUITARPIEZOELECTRIC TRANS- DUCER BRIDGE WITH REPLACEABLE STRING HEIGHTADJUSTORS Robert C. Scherer, Cincinnati, Ohio, assignor to D. H. BaldwinCompany, Cincinnati, Ohio, a corporation of Ohio Continuation-impart ofapplication Ser. No. 483,679, Aug. 30, 1965. This application Apr. 23,1968, Ser. No. 723,535

Int. Cl. G10d 3/04, /00

U.S. Cl. 84-116 Claims ABSTRACT OF THE DISCLOSURE CROSS REFERENCES Thisapplication is a continuation-in-part of my application, Ser. No.483,679, entitled Electric Guitar Bridge, filed Aug. 30, 1965, now US.Pat. No. 3,396,284 issued Aug. 6, 1968, and assigned to the assignee ofthis application.

BACKGROUND OF THE INVENTION Electric guitars are conventionally providedwith transducers, capable of providing output in response to thevibrations of the strings when the latter are picked or plucked. In suchguitars the modes of vibrations of the strings vary with time, frominitial excitation to final decay, and, in particular, picking orplucking a string may induce a vibration in one plane in space while thefree vibration in one plane in space while the free vibrations of thestring may be in another plane, or the plane may oscillate in space,depending on the precise character of the excitation.

Guitar players desire that the sound of an electric guitar be similar tothat of an acoustic guitar, but the conventional electromagnetictransducers employed in electric guitars are not capable of respondingto all planes of vibration of a string, and usually can respond only tovertical vibrations, whereby the initial excitation of the string, whichis predominately horizontal, is lost. Nor can such transducers operatein conjunction with nylon or other non-metallic strings.

It is a function of the present invention to provide a stringtransducer, especially for an electric guitar, which responds tovibrations of a string occurring in any plane, and which respondsequally well to metallic and nonmetallic strings.

My prior application discloses an aluminum extrusion of U-shapedtransverse cross section, one arm of which is supported on a guitarbody, and the other arm of which has slots to define separatecantilevers for each string of the guitar. Piezoelectric transducers areprovided under each cantilever. The slots acoustically isolate theseveral strings, and the several cantilevers. Provision is made forstring length adjustment, and each cantilever is provided with a stringlocating notch.

It is found that the sophisticated musician desires individualadjustment of string heights. Such adjustment can be provided by filingthe bone to adjust individual string heights. The difiiculty ensues thatif the bone is overfiled the entire bridge must be discarded. Thepresent invention concerns itself with providing a nylon or otheracoustically isolating readily filable element, as part of the bridge,which can have its height individually formed, to adjust string heightson an individual or group basis, and which can be readily replaced ifdesired. Provision is additionally made for closely coupling the bridgeacoustically to the body of the guitar via a wooden spacer, whileproviding for screw adjustment of the extrusion bridge with respect tothe spacer.

Briefly describing a preferred embodiment of the invention, an elongatedmetallic extrusion is provided, having the cross section of a U. One armof the U forms a base which is supported on the body of a guitar, at theusual bridge location. The other arm is arranged to provide pluralcantilever arms, for separately supporting each string of the guitar.Considering one string only, for simplicity of explanation, apiezoelectric crystal is placed between the base and a cantilever arm.Overlying the crystal is a thin sheet copper; i.e. shim stock or thelike. Underlying the crystal is a further shim and under the latter is asheet of insulation whichhas acoustic damping properties. The two coppersheets then make contact with the electrodes of the crystal and can beconveniently connected to output leads.

SUMMARY OF THE INVENTION A transducer string bridge includes provisionfor string length adjustment while enabling close acoustic coupling ofthe transducer to the body of the guitar, and also provision forindividual string height adjustment in terms of a readily replaceablenylon filament on which the strings rest, the filament providingoperatively negligible acoustic coupling between strings. o

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of one specificembodiment thereof, especially when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a view in perspective of a guitar having a transducer bridgeaccording to the invention;

FIG. 2 is a view in perspective of a transducer bridge assemblyaccording to the invention;

FIG. 3 is a view in plan of the transducer bridge assembly of FIG. 2;

FIG. 4 is a view in transverse cross section taken on the line 4-4 ofFIG. 3; and

FIG. 5 is a view in transverse cross section taken on the line 55 ofFIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to theaccompanying drawings, 10 is an elongated extrusion, which may be madeof aluminum, brass, or the like, and which has a U-shape when taken incross section. Arm 11 of the U is a base arm. The further or upper arm14 of the extrusion is provided with transverse slots 15, which extendinto the end wall 10a, of the U, and form plural cantilever arms 14a. Anin verted V-shaped riser 17 is provided near the forward edge of eacharm 14a.

The cantilever arms form individual supports for the strings, which areacoustically largely isolated from one another by the slots 15.

Located under each cantilever arm 14a is a piezoelectric crystal 20.Under the crystals is a strip of thin shim stock 21. Under each strip ofshim stock 21 is a strip 22, of

insulation, which is resilient mechanically and which damps acousticvibrations. Overlying crystal 20 is a further strip of shim stock 23.Strip 21 thus forms one electrode for all of crystal 20, and strip 23,grounded to the extrusion, forms the other electrode. Leads 25 areconnected to strips 21 and 23.

The use of acoustic damping material 22 is particularly importantbecause it serves to damp out undesirable highs, as clicks, pops, fingernoise and the like, and also serves to acoustically isolate the crystals20 from one another.

The transducer bridge is slidably mounted on a wooden base plate 16,which is in turn glued to the instrument. Screw adjusting means 41, 41aare provided for longitudinally adjusting the position of the transducerbridge 10 with respect to the base plate 16, by turning nuts 41a onbolts 41.

Longitudinal grooves 42, of generally rectangular crosssection, are cutin the cantilevers 14a, in which is fitted a nylon filament 43. Thelatter is about A in width, and snugly fits the grooves 42. The filament43 is sometimes called a bone. It possesses a high degree of acousticinsulation longitudinally, so that crystals remain acoustically isolatedfrom each other. In the thickness mode, however, the filament 43 closelycouples the strings 44 to the cantilever 14a, and thence to the body ofthe guitar.

A wooden string support 40 includes two wings 45, 46 which are cementedto the body of the guitar G. The extrusion 10 extends between the wings45, 46, resting on a wooden spacer 16, which in turn rests on the bodyof the guitar, and behind the extrusion 10 is located a wooden bridgingmember 47, integral with wings 45, 46, resting on and cemented to thebody of guitar G. Extending rearwardly of the extrusion 10 are the twobolts 41, which are immovable with respect to the extrusion. Thebridging member 47 includes horizontal apertures 50, through which bolts41 extend, into a rearward slot 51. The bolts 41 are immovably securedto the extrusion 10 by means of vertical pins 52, extending through theextrusion 10 and also through the bolts 41.

Nut 41a, pertaining to the screws 41, extend into the slot 51. Byturning the nuts 41a the screws 41, and similarly the extrusion 10, maybe moved longitudinally of the guitar G, to adjust string length.

The bridging member 47 also includes openings 55 for the strings 44,through which the strings extend and are knotted around the bridgingmember 47.

The extrusion 10 may be potted with soft rubbery material, which doesnot appreciably reduce amplitude of vibrations of the crystals 20, butwhich does maintain the elements of the transducer in place and enhanceits aesthetic appeal. Suflicient pressure exists on the crystals 20 toassure that these will operate linearly with respect to vibrationsimparted thereto.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variation of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What is claimed is:

1. In a transducer bridge for a stringed instrument,

an aluminum extrusion of U-shaped transverse crosssection, said aluminumextrusion providing a base,

means for supporting said base on said stringed instrument,

said aluminum extrusion providing discrete cantilever arms extendingparallel to said base, there being one cantilever arm for each string ofsaid stringed instrument,

a separate piezoelectric element located between each cantilever arm andsaid bridge and compressed therebetween,

means for deriving voltages from said piezoelectric elements which aredeveloped in response to vibrations of said strings and are communicatedto said piezoelectric elements via said cantilever arms, and

a filament extending lengthwise of said cantilever arms and locatedbetween said strings and said cantilever arms,

said filament having operatively negligible lengthwise acoustic couplingand being sufficiently soft that string height may be readily adjustedby removing material from the filament,

said cantilevers including lengthwise of said extrusion a groove forlocating and retaining said filament.

2. The combination according to claim 1 wherein is provided anon-metallic separator located between said base and said stringedinstrument, and

screw means for adjusting the longitudinal position of said transducerbridge with respect to said string instrument.

3. In a transducer bridge for a stringed instrument,

a U-shaped elongated metallic member,

one of the arms of said member providing a flat base,

the other of the arms of said member being slotted to provide aplurality of cantilever arms extending parallel to said base,

a piezoelectric crystal element located intermediate each of saidcantilever arms and said base and in contact with both one of saidcantilever arms and said base,

a layer of electrically conductive material underlying and in contactwith said piezoelectric elements,

an electric and acoustic insulating layer underlying said layer ofelectrically conductive material,

a further layer of electrically conductive material overlying saidcrystal and in contact with said cantilever arms, and

string loacting filamentary means extending longitudinally of saidcantilever arms and supported thereby and separable therefrom.

4. The combination according to claim 3, wherein said filamentary meansis a single filament.

5. The combination according to claim 3, wherein said filamentary meansis a nylon filament.

'6. The combination according to claim 3, wherein said filamentary meansis sufliciently soft that string height may be readily selected byremoving material from said filamentary means to desired extendsindividual to each string.

7. The combination according to claim '6, wherein said cantilever armsinclude longitudinal grooves for locating said filamentary means.

'8. In a transducer assembly for a stringed instrument,

a wooden element extending transversely of said instrument and cementedthereto,

said wooden element including two wings separated by a bridging element,

an acousto-electric transducer bridge for said strings extending betweensaid wings and movable with respect to said instrument, and

screw threaded means engaging said transducer bridge and said bridgingelement for moving said transducer With respect to said bridgingelement, thereby to adjust the eifective lengths of the strings of saidstringed instrument,

wherein said acousto-electric transducer bridge includes an extrusion ofU-shape in transverse section, and

acousto-electric transducers positioned between the arms of saidextrusion, the strings of said instrument resting on one arm of saidextrusion and the other arm resting on said instrument, and

slots in said one arm defining individual cantilevers for each of saidstrings.

9. The combination according to claim 8 wherein is provided filamentaryinterposer means located between said string and said one of said arms.

10. The combination according to claim 8, wherein said bridging elementincludes apertures through which said 6 strips extend, ends of saidstrings being secured to said 3,301,936 1/1967 Carman et a1 841.16bridging element. 3,396,284 8/1968 Scherer 3108.3

References Cited 931689 s/l ggj G PATENTS UNITED STATES PATENTS 52,764,052 9/ 1956 McBride 84-1.15 WARREN E. RAY, Primary Examiner3,066,567 12/1962 Kelley 84l.16 3,073,203 1/1963 Evans 841.16

